put GPUZ and CPUZ up on the second screen while in a 3D application and check to see if the clock frequencies drop
That's the first step. Verify whether or not clocks are dropping. If clocks are dropping, the most common culprit is thermal throttling. What program/s can overlay GPU temp and clock info on top of the game screen? I know they're out there.
You can most likely reproduce this throttling effect with Prime95
(will load your CPU to 100%) and/or MSI Kombustor
(either program will load your GPU to 100%) to name a couple. Using a stress testing program will allow you to use temperature/clock monitoring programs like CPUz and GPUz in front of the stress testing window. (hepful if you only have one monitor) Stress testing programs will give you a constant load and eliminate any possible in-game issues that may be causing these problems. (isolate the variables)
If throttling is happening, you'll need to get the possible overheating issue isolated.
1) take the side panel off your case
2) clean the GPU & CPU heatsink with canned air
3) set a box fan or ~9" round fan next to your case, pointing into the case. If you can, lock the CPU and GPU fans to 100%
That should give you the best chance of avoiding clock throttling due to any overheating issues.
Report back once you've tried these.
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